1. Field of the Invention
The present invention relates to a polishing method for polishing a surface of a material to be polished and a fabrication method of a thin film magnetic head having a planarization process for planarizing the surface of the material to be polished by polishing.
2. Description of the Related Art
In a fabrication of a thin film magnetic head used for reading and writing heads of a magnetic disk drive, a chemical mechanical polishing (hereinafter, a CMP) is used for forming a surface with a high flatness. In the CMP, first, a polishing surface of a polishing pad covered on a rotating polishing surface plate and a surface to be polished of a substrate which is a material to be polished supported by a polishing head contact with pressure. Supplying slurry, which is an abrasive material, on the surface to be polished of the polishing pad and rotating each of the polishing pad and the polishing head, the surface to be polished is polished chemically and mechanically by supplying the slurry between the polishing pad and the surface to be polished. By the polishing using this CMP, a desired flatness can be achieved at a global area as well as at a local area.
Elastic bodies such as a foaming urethane which, for example, is a porous material and has fine irregularities on a surface thereof are used for the polishing pad. Therefore, during the polishing, the polishing surface of the polishing pad copies a shape (irregularities) of the opposing surface of the material to be polished and contacts to substantially the whole surface of the material to be polished. Therefore, in a surface plate polishing by a general mechanical polishing, the polishing pad only strikes protruding portions on the surface to be polished, thereby polishing substantially only the protruding portions. On the other hand, in the polishing by the CMP, the polishing on a surface at a lower position is also proceeded because the polishing surface of the polishing pad contacts to the surface at the position lower than the protruding portion. However, since a contact pressure with the polishing surface of the polishing pad is greater at the protruding portion than the surface at the lower position, the protruding portion is polished relatively faster, thereby the planarization of the surface to be polished is proceeded.
The conventional planarization process using the CMP in the fabrication process of the thin film magnetic head is briefly described with reference to FIG. 24. FIG. 24 shows a cross section of a substrate which is obtained by cutting a pole portion of the thin film magnetic head in parallel with a track plane. As shown in FIG. 24, an insulating layer 62 which is a lower layer made of alumina (Al2O3) is formed on an AlTiC substrate 60 and a bottom shielding layer 64 which is approximately 3 xcexcm in thickness and made of permalloy is formed thereon. It will be noted that the two bottom shielding layers 64 are shown in FIG. 24.
In order to planarize the upper surface of the bottom shielding layer 64, as shown FIG. 24, alumina is deposited on the whole surface of the substrate and the bottom shielding layer 64 is embedded and coated by forming a coating layer 66 having 4.5 xcexcm in thickness which is 1.5 times thicker than the film thickness of the bottom shielding layer 64. At this time, the coating layer 66 over the bottom shielding layer 64 which is a thin film pattern is a protrusion of 7.5 xcexcm in height from the insulating layer 62.
Thus, after embedding and coating the surface of the substrate 60, on which the bottom shielding layer 64 which is the thin film pattern is formed, by the coating layer 66, the polishing by the CMP is started as it is. After the upper portion of the bottom shielding layer 64 of the thin film pattern is exposed from the coating layer 66 by the polishing by the CMP, the polishing is further proceeded to form a planarized layer with a predetermined film thickness. Thus, in the planarization process of the thin film magnetic head, a protrusion due to the coating layer is formed at the upper portion of the thin film pattern when the coating layer is formed on the surface of the substrate. Therefore, in order to form the planarized layer with a desired film thickness, the coating layer is required to be planarized by polishing as much protruding portion as possible before the upper portion of the thin film pattern exposes from the coating layer. Therefore, in the conventional planarization process using the CMP in the fabrication process of the thin film magnetic head, the film thickness of the deposited coating layer is required to be formed quite thick.
For example, when the upper surface is planarized after an element having a film thickness of 2xcx9c10 xcexcm is embedded and coated with the coating layer made of alumina, as described above, the film thickness of the coating layer is required to be fabricated approximately 1.5 times thicker than the film thickness of the element in the conventional polishing method according to the CMP method. Therefore, the height of the coating layer which is the upper portion of the element to be the protrusion is equal to 3xcx9c15 xcexcm from the insulating layer 62.
When almina which is the coating layer deposited to such thickness is largely removed by the polishing by the CMP, the variations of the removal amount inevitably become large and consequently the variations of the residual film thickness on the surface of the material to be polished after the polishing becomes large. In short, according to the planarization by the conventional CMP, the variations of heights on the surface to be polished can not be reduced, thereby resulting in the cause of the reduction in yield in the element fabrication.
Further, in the fabrication process of the conventional thin film magnetic head, the fabrication process for the coating layer in the planarization process is time-consuming and therefore leads to an inhibitory factor for improving a throughput of the element fabrication.
An object of the present invention is to provide a polishing method for reducing the variations of a residual film thickness on the surface of a material to be polished after polishing.
Another object of the present invention is to provide a fabrication method for reducing the time required for a polishing process.
A further object of the present invention is to provide a fabrication method of a thin film magnetic head which improves a yield of the element fabrication by reducing the variations of the residual film thickness on a surface of the material to be polished after polishing.
A furthermore object of the present invention is to provide a fabrication method for a thin film magnetic head which improves a throughput of the element fabrication by reducing the time required in a polishing process.
Above objects are achieved by a polishing method of polishing a surface of a material to be polished comprising the step of polishing the surface after reducing a film thickness at a protruding portion formed on the surface.
Also, the polishing method of this invention comprises the steps of patterning an etching protection film after forming the etching protection film on the surface, opening the etching protection film over the protruding portion and reducing the film thickness of the protruding portion by etching.
Further, in the polishing method of this invention, the protruding portion is formed on a coating layer over the thin film pattern, the coating layer coats and embeds the thin film pattern formed on the material to be polished. Furthermore, the etching protection film is formed on the coating layer.
In the polishing method of the present invention, the etching is an isotropic etching. Also, the etching protection film is made of photoresist or the etching protection film is made of a metal material.
Further, in the polishing method of the present invention, the opening is formed to have a width equal to or narrower than a width of the thin film pattern or the opening is formed to have a width substantially equal to the length obtained by reducing the double thickness of the film of the thin film pattern from the width of the thin film pattern.
Furthermore, in the polishing method of the present invention, the coating layer is formed to have a film thickness equal to or thicker than the film thickness of the thin film pattern. At the same time, the coating layer is formed of an insulating material. Also, in the polishing method of the present invention, the polishing method comprises the step of polishing the surface by a chemical mechanical polishing after reducing the film thickness of the protruding portion.
The above objects are achieved by a fabrication method of a thin film magnetic head having a planarizion process for planarizing a surface of a material to be polished by polishing comprising the planarization process having any polishing method in the present invention. The planarization process is performed to at least any one of surfaces of a plurality of magnetic layers structuring the thin film magnetic head. Further, the plurality of the magnetic layers includes at least one of a bottom shielding layer, a top shielding layer, and upper pole portion which structure the thin film magnetic head.